Spark plug and method of manufacturing same



Feb. 24, 1959 E. w. PIERCE 2,875,365

SPARK PLUG AND METHOD OF MANUFACTURING SAME Filed Jan. 26, 1954 INVENTORUnited States Patent SPARK PLUG AND METHOD OF MANUFACTURING SAME Earl W.Pierce, Flint, Mich., assignor to General Motors Corporation, Detroit,Mich., a corporation of Delaware Application January 26, 1954, SerialNo. 406,171 7 Claims. ((31.313-145) This invention relates to a sparkplug and the method for manufacturing same and more particularly to anangle type shielded spark plug and to the method of centralizing andsealing a warped insulator in the spark plug shell.

In the manufacture of spark plugs a relatively elongated ceramicinsulator body is used to insulate the center electrode from the plugshell which acts as the grounding portion of the ignition system. Suchinsulators are commonly formed by pressure molding theceramic powderinto a blank having the desired configuration followed by a firingoperation to sinter the ceramic powder into a fused unitary body. It hasbeen found that the ceramic blanks are generally warped or otherwisedistorted during the firing operation with the result that the axis ofthe center electrode counterbore is no longer a straight line throughthe center of the two axial extremities of the insulator.

Assembly of a spark plug with such an insulator results in the eccentriclocation of the center electrode with respect to the shell or groundelectrode. a serious problem where it is necessary to accurately controlthe centrality of the insulator. This problem is especially acute in themanufacture of aviation type spark plugs wherein the outer or groundelectrode is generally the annular end of the plug shell. Likewise, thedistortion frequently precludes the insulator seating squarely withinthe plug shell. Under these conditions it is practically impossible toattain the desired pressure seal of the insulator within the plug shellwithout resort to high. sealing pressures which tend to break the bodyof theinsulator, and the use of exceedingly thick and soft gasketmaterials such as metal foils which increase the cost and probability ofseal failure. The unequal application of sealing pressure to theinsulator likewise increases the probability of insulator breakage.

Insulator distortion presents a further problem where the insulator isof the angle type, that is, where a cable receiving portion is formedintegral with and at an angle to the upper end of .theelectrode portionand is used with a spark plug body of corresponding angle configurationsurrounding the entire insulator as an electrical shield, the shieldbeing in close adjacency with the outer end of the cable portion of theinsulator. The distortion of the insulator may be such that, as measuredin a plane passing through the center of the outer end of the cableportion of the insulator and parallel with the axis through the centerof the two axial extremities of the insulator, the distance between thecable portion center and upper extremity of the insulator issufiiciently different from that provided for in the metal shell as topreclude the assembly of the upper or shield portion of the spark plugbody about the insulator without causing the insulator cable portion tobreak.

It is therefore an object of my invention to provide a method forcentralizing a spark plug insulator in a simple and inexpensive manner.

It is another object of my invention to provide a method This presents2,875,365 Patented. Feb. .24, .1959

2 for assuring the proper seating of a spark plug insulator within thespark plug shell for attaining the desired pressure seal.

It is another object of my invention to provide a method for simply andinexpensively centralizing a spark plug insulator within a spark plugshell and for properly seating the insulator therein.

It is another object of my invention to provide an angle type insulatoradapted for concentric and proper seating within a spark plug shellhaving a metallic shield portion formed as an integral part of the upperportion of the shell.

It is another object of my invention to provide an angle type shieldedspark plug wherein the plug body and insulator are each formed withunitary correspondinlgy shaped angularly arranged portions.

To attain these objects, I provide a metal gasket adapted to be fittedon the locating surfaces of the insulator following which I rotate theinsulator on an axis through the center of its two axial extremities topermit machining of the surfaces of the gasket concentric and true withthis axis. The compensated insulator is then positioned in the sparkplug shell and the remaining portions of the plug body are secured tothe shell to form a unitary shielded spark plug.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawing, where in a preferred form of the present invention is clearlyshown.

In the drawing:

Figure 1 is a diagrammatic vertical section with parts broken away ofthe insulator of my invention showing the metal compensating membersboth before and after machining.

Figure 2 is a sectional view on line 2-2 of Figure 1 showing the degreeof distortion in the insulator.

Figure 3 is a sectional view with parts broken away of the spark plug ofmy invention.

Referring now to the drawing and more particularly to Fig. 3, there isshown an angle type spark plug 1 embodying the several features of myinvention. Plug 1 comprises a cylindrical main portion or shell 3 havinga longitudinal bore 5 therein, the upper portion '7 thereof beingcounterbored to form a shoulder E The edge of shoulder 9 is beveled toprovide a conical seating ledge 11 having an axis coincident with theaxis of shell 3. The bottom portion 13 of shell 3 serves as the outer orground electrode and is annular in configuration. Seating ledge 1] actsboth to support the spark plug insulator with its tip end concentricwith the outer electrode 13 and as an abutment for establishing a sealbetween the insulator and the shell 3.

Shell 3 is provided with an annular groove 15 on its outer surfaceadjacent shoulder 9 to enable a gas-tight seal between the shell andinsulator by means of the Cico weld process wherein, under the influenceof axial pressure and electrical heating, the shell thermoplasticallycollapses in the annular thin wall section 15 to clamp the insulator onledge 11.

The upper end of shell 3 adjacent groove 15 is necked down to provide ashoulder 17 on which a metal mounting pad '19 is telescopicallypositioned. Pad 19 serves to provide the means for mounting theassembled plug in the engine and at the same time provides an extensionof the shell 3 for shielding the plug.

The metal plug body and electrical shielding of plug 1 is completed bymeans of metal shield cap 21 and shield sleeve 23, these elements beingshown as telescopically fitted to each other and to pad 19. The severalbody portions 3, 19, 21 and 23, are securely attached to each otherinany suitable manner, i. e., welding, to form a single unitarystructure.

It should be noted that in the particular embodiment shown on thedrawing, the cap 21 abuts the top of the insulator and cooperates withledge 11 in a manner fully disclosed hereinafter to clamp the insulatorin the plug body and provide a gas-tight seal therebetween. Cap 21 is ofsuch configuration as to provide, together with mounting pad 19, a sideopening in the plug body in which sleeve 23 is adapted to be positioned,its axis extending transversely to the axis of the shell 3.

Having reference now to Figs. 1 and 3, a ceramic insulator 25, having acenter electrode 27 positioned therein, is mounted within the metal bodyin a manner fully disclosed hereinafter as to position the electrodeconcentric with the outer electrode 13, bottom portion of shell 3.Insulator 25 is generally cylindrical in shape and has a generallytapered lower section 29 and a raised upper section 31. Section 31provides a lower shoulder 32 and a generally circular top surface 32serving as an upper shoulder. A tubular section 33 extends laterallyfrom the raised section 31. Insulator 25 is provided with asubstantially concentric bore 35 extending from the firing end 37 ofsection 29 to Within the upper portion of raised section 31. A laterallyextending bore substantially concentric with section 33 is provided tointersect the upper end of bore 35 and form a recess 39 in which a metalcontact cap 41 is adapted to be positioned. A counterbore 43 is providedin section 33 and is adapted to receive an insulated ignition cable 45.

The electrical connection between cable 45 and center electrode 27 isassured by inserting the inner end of the electrode into a correspondingopening in cap 41. The

end of the electrode may be either threaded as shown or slotted to formeither a threaded or a spring-like friction connection with the cap. Theconductor 47 of cable 45 is retained in contact with the outer end ofcap 41 in any of a number of ways which are Well known in the art andform no part of the present invention. Any spaces in cap recess 39 andaround electrode 27 are filled with a sodium silicate-kaolin type cementalso well known in the art. The cement seems to both seal and retain theelectrode in the insulator.

As shown on the drawing, novel means are provided to compensate for thewarpage and deformation of the insulator 25 that occurs in the firingoperation and to assure (l) the centrality of the center electrode, (2)the formation of a gas-tight seal between the insulator and the sparkplug hollow metal body without the use of excessive pressures and (3)the positioning of the outer end of the laterally extending section ofthe insulator substantially concentric within the sleeve portion of theplug body.

Having particular reference now to Fig. 1, insulator 25 is shown ashaving a distorted axis aa as a result of firing. It is to be understoodthat the bending and distortion of the insulator upon firing is not asextreme as shown on the drawing but that it is nevertheless sufiicientto destroy the concentricity and alignment of the surface of section 31and shoulders 32 and 32 with respect to axis AA through the center ofthe two axial extremities 32' and 37 of insulator 25.

In order to compensate for this misalignment, a generally cup-shapedgasket 49 having a conical bottom portion 51 corresponding to conicalshoulder 32 is securely attached to the lower portion of section 31.Gasket 49 is made of such relatively soft metal as nickel or copper andmay be attached to the insulator in any suitable manner, i. e.press-fitted, shrink-fitted, etc. It is to be understood that the gasketmay be secured on the insulator by building it up on the insulator bysuch methods as electrodeposition or spraying. Insulator 25 is thenpositioned in a lathe to revolve about axis AA passing through the truecenter of axial extremities 32 and 37. The side wall of gasket 49 isthen turned down concentric with axis A-A and to a diametercorresponding to that of the counterbored portion 7 of shell 3 in whichit is to be mounted. In this manner, the centrality of the centerelectrode 27 is assured. At the same time, the conical surface ofportion 51 is turned down true with axis AA, that is, the turned conicalsurface of portion 51 has its generating axis coincident with axis AA.In this manner, a gas-tight seal is assured between the insulator 25 andshell 3 since the surface of portion 51 is turned down to correspond toconical seating ledge 11. As shown on Fig. 1, the dashed outline ofgasket 49 denotes its original dimensions with its surface eccentric andin misalignment with axis AA. The solid outline of gasket 49 is itsfinal configuration after machining to make its surface concentric withaxis AA.

As described above, a gas-tight seal between insulator 25 and shell 3 isobtained by applying pressure to shield cap 21 which collapses thethinned-out portion of shell wall 3 in annular groove 15, cap 21 thenacting to clamp insulator shoulder 32 on ledge 11 with bottom portion 51of gasket 49 therebetween. In order that the sealing pressure may beapplied evenly to the surface of insulator shoulders 32 and 32 and thuspreclude insulator breakage otherwise resulting, a cap or gasket member53 made of nickel or copper is secured to top surface 32 in a mannersuch as that used with gasket 49. Insulator 25 is then mounted in alathe to revolve about axis AA and the surface of member 53 is turneddown to square it olf or make it true with the axis of revolution. Atthe same time, the amount of metal machined off gasket 53'is controlledto compensate for the Warpage in laterally extending section 33 andasure that its outer end will be positioned substantially concentricwithin sleeve 23 when cap 21 and sleeve 23 are assembled about theinsulator.

In order to facilitate the ready understanding of the principles of myinvention, the following is a concise description of the production of aspark plug as shown on the drawing. The several metal parts of sparkplug body 3, 19, 21 and 23, are accurately machined so that theirseveral seating and wall surfaces are concentric and true with thelongitudinal axis of shell 3 as well as being so dimensioned as to fittogether telescopically with sleeve 23 at a predetermined angle to shell3. The angle type ceramic insulator 25 is then molded of a suitable heatresisting powder following which the molded blank is fired to sinter itinto a composite fused body. Centralizing gasket 49 is then pressed onthe lower end of raised section 31 and its surfaces are turned downconcentric and true with axis AA through the true center of insulatorextremities 32 and 37. Insulator 25 is then gaged for the desiredangular positioning of laterally extending section 33 to the axis ofrotation AA. Distortion of such nature acts to change the distancebetween the center of the outer end of section 33 and the surface ofupper extremity 32' with resultant breakage of section 33 upon assemblywith sleeve 23. The deviation in this distance from standard is noted.Cap or gasket member 53 is then pressed on the upper end of raisedsection 31 and its surface 32 is turned down square with axis AA and anamount sufficient to compensate for the deviation above noted thusassuring concentricity of the outer end of section 33 in sleeve 23. Theinsulator is then positioned in shell 3 squarely on ledge 11 with thecenter electrode concentric with the annular ground electrode 13. Theremaining body parts are then telescopically assembled on the shell andthe assembly is placed in an oven at about 2000 F., the interlockingsurfaces of the several parts having been previously coated with acopper brazing paste. On cooling, the assembly is formed into a unitary,completely shielded subassembly. The gas-tight seal of the insulator 25within shell 3 is accomplished by mounting the plug 1 in a jig forsupporting the shell 3 While provided a simple and integrally formedshielded angle spark plug by a method of fabrication whichpermits theassembly of spark plugs to dimensional limits heretofore not possiblebecause of excessive warpage which is inherent in most spark pluginsulators. At the same time, the even application of sealing pressureto the shell is made possible thus reducing insulator breakage both inassembly and in field use.

I have described my invention as applied to an angle typeplug. However,I wish it to be understood that it is equally applicable to straighttype spark plugs. In such a plug the upper portion of raised section 31may have the same configuration as the lower portion and a gasket membersimilar to contralizinggasket 49 may be used.

While the form of embodiment of the ,invention as herein disclosed,constitutes a preferred form, it is to be understood that other formsmight be adopted as may come within the scope of the claims whichfollow.

What is claimed is:

1. In an angle type unitary spark plug, the combination of a metal shellthe bottom portion of which constitutes an annular ground electrode andhaving a seating ledge on its inner surface, a tubular metal memberhaving angularly arranged portions secured to the top of said shell toform an angular tubular unitary metal body, an angle type ceramicinsulator having a configuration generally corresponding to that of theinner surface of said body positioned therein, said insulator having alower section and a raised upper section providing an upper and lowershoulder and a section extending laterally outward from said raisedsection and integral therewith, an axial bore in said upper and lowersections, a connecting axial bore in said laterally extending section, acenter electrode secured in said first-mentioned bore, a metalcentralizing member secured on the lower portion of said raised sectionand having its surface concentric and true with an axis through thecenter of the two axial extremities of said insulator, and a metalmember on the upper end of said raised section having its surface truewith said axis, the inner top surface of said tubular metal member beingin abutment with said metal member to clamp said insulator on said ledgewith substantially evenly distributed pressure in gas-tight relationshipwith said shell, said center electrode being accurately locatedconcentric with said annular ground electrode, and the outer end of saidlaterally extending section being substantially concentric with saidshield sleeve.

2. In an angle type unitary spark plug, the combination of a cylindricalmetal shell the bottom portion of which constitutes an annular groundelectrode and having a seating ledge on its inner surface, a mountingpad secured to said shell, a shield cap secured on the top of said shelland having a side opening formed therein, a shield sleeve secured withinsaid opening at an angle to said shell to form an angular tubularunitary metal body, an angle type ceramic insulator positioned withinsaid body and having a configuration generally corresponding to that ofthe inner surface thereof, said insulator having a lower section and araised upper section providing an upper and lower shoulder and a sectionextending laterally outward from said raised section and integraltherewith, an axial bore in said upper and lower sections, a connectingaxial bore in said laterally extending section, a center electrode insaid first-mentioned bore extending into said connecting bore, a metalcentralizing gasket secured to the lower portion of said raised sectionand having its surface concentric and true with an axis through thecenter of the two axial extremities of the insulator,

and a metal gasket on the upper end of said raised section and havingits surface true with said axis, the inner top surface of said shieldcap being in abutment with said metal gasket to clamp said insulator onsaid ledge with substantially evenly distributed pressure and ingastight relationship with said shell, said center electrode beingaccurately located concentric with said annular ground electrode, andthe outer end of said laterally extending section being substantiallyconcentric with saidv shield sleeve.

3. In an angle type unitary spark plug, the combination of a cylindricalmetal shell the bottom portion of which constitutes an annular groundelectrode and having a conical seating ledge on its inner surface, amounting pad telescopically secured to the top of said. shell, a shieldcap telescopically secured to said pad and cooperating therewith to forma side opening, a shield sleeve secured within said opening at an angleto said shell to form an angular tubular unitary metal body, an angletype ceramic insulator positioned within said body and having aconfiguration generally corresponding to that of the inner surfacethereof, said insulator having a generally tapered lower section and araised upper section providing an upper and lower shoulder, and having asection extending laterally outward from said raised section andintegral therewith, an axial bore in said upper and lower sections, aconnecting axial bore in said laterally extending section, a metalcontact cap in said connecting bore, a center electrode in saidfirst-mentioned bore, said electrode having threaded engagement withsaid contact cap, a generally-cup-shaped metal centralizing gasketpressed on the lower portion of said raised section and having its walland bottom surface concentric and true, respectively, with an axisthrough the center of the two axial extremities of the insulator, and ametal gasket on the upper end of said raised section and having itssurface square with said axis, the inner top surface of said shield capbeing in abutment with said metal gasket to clamp said insulator on saidledge with substantially evenly distributed pres sure and in gas-tightrelationship with said shell, said center electrode being accuratelylocated concentric with said annular ground electrode, and the outer endof said laterally extending section being substantially concentric withsaid shield sleeve.

4. In an angle type unitary spark plug, the combination of a metal shellthe bottom portion of which constitutes an annular ground electrode andhaving a seating ledge on its inner surface, a mounting pad secured tosaid shell, a shield cap secured on top of said shell and having a sideopening formed therein, a shield sleeve secured within said opening atan angle to said shell to form an angular tubular unitary metal body, anangle type ceramic insulator having a configuration generallycorresponding to that of the inner surface of said body positionedtherein, said insulator having a lower section and a raised uppersection providing an upper and lower shoulder and a section extendinglaterally outward from said raised section, said sections being formedas an integral unitary body, an axial bore in said upper and lowersection, a connecting axial bore in said laterally extending section, acenter electrode in said first-mentioned bore having its upper endpositioned in said connecting bore, the inner top surface of said shieldcap being in abutment wtih said insulator to clamp said lower shoulderon said ledge in gas tight relationship with said shell, said centerelectrode being accurately located concentric with said annular groundelectrode and said insulator being substantially centralized within saidbody.

5. In an angle type unitary spark plug, the combination of a cylindricalmetal shell the bottom portion of which constitutes an annular groundelectrode and having a conical seating ledge on its inner surface, acylindrical mounting pad telescopically secured to the top of saidshell, a shield cap telescopically secured to said pad and cooperatingtherewith to form a side opening, a shield sleeve secured within saidopening at an angle to said shell to form an angular tubular unitarymetal body with said shell, an angle type ceramic insulator positionedwithin said body and having a configuration generally corresponding tothat of the inner surface thereof, said insulator having a generallytapered lower section and a raised upper section providing an upper andlower shoulder and a section extending laterally outward from saidraised section, said sections being formed as an integral unitary body,an axial bore in said bore in said upper and lower section, a connectingaxial bore in said laterally extending section, a metal contact memberin said connecting bore, a center electrode in said first-mentioned boresecured to said contact member the inner top surface of said shield capbeing in abutment with said insulator to clamp said lower shoulder onsaid ledge in gas tight relationship with said shell, and said centerelectrode being accurately located concentric with said annular groundelectrode.

6. In the manufacture of a spark plug having an angle type unitary metalbody and a correspondingly shaped insulator, said insulator having agenerally tapered lower section, a raised upper section providing anupper and lower shoulder, and a section extending laterally outward fromthe raised section, intersecting axial bores being provided in the upperand lower sections and in the laterally extending section, the steps ofmolding the insulator blank of suitable material, firing said blank tosinter said material into a. composite structure, pressing a metalcentralizing gasket on the lower end of the insulator raised section,positioning said insulator in a lathe to revolve about an axis throughthe center of its two axial extremities, turning down the surface ofsaid gasket concentric and true with said axis, pressing a metal gasketon the upper end of said insulator raised section and turning down itssurface true with said axis an amount necessary to compensate for anywarpage present in said laterally extending section, positioning thethus compensated insulator in the spark plug shell, assembling amounting pad, shield cap and shield sleeve on the shell and about saidinsulator, applying end pressure to said shell through said shield capto collapse an annular portion of the shell and clamp said insulator ingas-tight relationship therewith, positioning the center electrode inthe boreof said upper and lower insulator sections with the upper end ofsaid electrode extending into the bore of said laterally extendingsection.

' 7. In the manufacture of a spark plug having an angle type unitarymetal body and a correspondingly shaped insulator, said insulator havinga generally tapered lower section, a raised upper section providing anupper and lower shoulder, and a section extending laterally outward fromthe raised section, intersecting axial bores being provided in the upperand lower sections and in the laterally extending section, the steps ofmolding the insulator blank of suitable heat resisting ceramic powder,firing said blank to sinter said powder into a composite structure,pressing a generally cup-shaped metal centralizing gasket on the lowerend of the insulator raisedsection, positioning said insulator in alathe to revolve about an axis through the center of its two axialextremities, turning down the wall and bottom surface of said gasketconcentric and true, respectively, with said axis, pressing a metalgasket on the upper end of said insulator raised section and turningdown its surface square with said axis an amount necessary to compensatefor any warpage present in said laterally extending section, positioningthe thus compensated insulator in the spark plug shell with its lowershoulder on a correspondingly shaped supporting ledge on the shell,telescopically assembling a mounting pad, shield cap and shield sleeveon the shell about said insulator, applying pressure to said uppershoulder through the shield cap to collapse an annular portion of saidshell and clamp said insulator in gas-tight relationship with the shell,positioning a contact cap in the bore of said laterally extendinginsulator section, positioning the center electrode in the bore of saidupper and'lower insulator sections, and securing said electrode to saidcontact cap by threaded engagement of said electrode in said cap.

References Cited in the file of this patent UNITED STATES PATENTSHastings et a1 Aug. 15, 1944

